Kinetic Salt Effects and Structure of the Aqueous Solution

Abstract

The salt effects in many reactions between anions are compared with the predictions of the Brønsted‐Debye theory, and with the assumption of formation of reactive ion pairs; both approaches appear to be inadequate. Clear evidence is available (change of activation energy, effect of organic ions, effect of complex ions) that at least part of the salt effects is non‐electrostatic in nature, so that the introduction of appropriate structural parameters in a general electrostatic treatment is required for their explanation. The Debye‐Hückel theory cannot be used as a frame for the introduction of such parameters, but a more flexible and self‐consistent theory is required. Evidence is presented that the Mayer theory can interpret thermodynamic properties even in cases where the Debye‐Hückel theory fails, and a method is suggested whereby the Mayer theory is used to interpret the salt effect and to give a structural meaning to the empirical parameters which must be introduced.

Kinetics of the reaction of the bis(oxalato)planinate(II) ion with thiocyanate

“…It is well known in fact that strong specific salt effects can be observed even when no appreciable amounts of ion pairs can be detected. 21 The Mg2+ ion has an accelerating effect on the second step which becomes 4 times faster than in the presence of the alkali metal cations. This is in agreement with the fact that the reaction of the second step involves a 4r ion, so that both the electrostatic and the nonelectrostatic effects are magnified.…”